Impact of ENSO events on meteorological drought in the Weihe River basin, China

El Nino-Southern Oscillation (ENSO) events influence elements of the terrestrial water cycle such as precipitation and temperature, which in turn have a significant impact on drought. This work assessed the impact of El Nino and La Nina on droughts from 1970 to 2020 in the Weihe River basin (WRB) in China. This study used a standardized precipitation index (SPI) to characterize meteorological drought. The regional drought response to extreme events in El Nino/La Nina was analyzed using principal component analysis (PCA), Wilcoxon and Mann-Whitney tests, and other methods. The results showed that, based on PCA, the WRB is divided into two regions, with the northwest region (67%) comprising more area than the southeast region (33%). El Nino/La Nina significantly impacted drought in the WRB. Droughts mainly occurred in the El Nino year and the year following La Nina. El Nino had the highest number of drought years (44%), followed by the year following La Nina (43%). The number of droughts was lowest in the year following El Nino (22%). At 1-, 3-, and 6-month timescales, significant droughts mainly occurred from July to December in El Nino years and the summer following La Nina. On a 12-month timescale, significant droughts mainly occurred from January to April in El Nino years, while no droughts occurred in La Nina years. The longer the timescale of the SPI, the more months of significant drought in El Nino years; however, the intensity of drought in the basin was reduced. In the year following La Nina, summer droughts intensified on a 6-month timescale compared to a 3-month timescale. El Nino and La Nina had greater impacts on the drought index in the northwest region of the WRB. In the northwest region, 60% of the months showed significant drought, compared to only 2% of the months in the southeast region. The drought intensity was higher in the northwest region. The results of this study provide a reference for drought management and early warning systems in the WRB and support solutions to water shortage.